1. Field of the Invention
The present invention relates to a substrate processing device, and in particular to a substrate processing device which is employed in the deposition of thin films using thermochemical reactions or plasma chemical reactions, or in etching applications using plasma chemical reactions.
2. Description of Related Art
More and more progress has recently been made in the miniaturization and the degree of integration of semiconductor elements in fields involving the manufacture of these elements. Many problems remain to be solved in the miniaturization of elements, such as precise miniaturization machining, sufficient film coating in microholes or at stepped portions, reducing the level difference in elements, preventing heat radiation caused by high current density, and preventing wire breakage caused by electromigration caused by high current density. Means that can be anticipated for resolving such problems include thermal CVD (chemical vapor deposition) devices with which thin films are deposited using chemical reactions, plasma CVD devices with which thin films are deposited using plasma chemical reactions, and reactive ion etching devices featuring the use of plasma chemical reactions. Here, both thermal CVD and plasma CVD devices are referred to as CVD devices for the sake of convenience. These CVD devices are described below.
The structure of the reactor in conventional CVD devices can be divided into asymmetrical and symmetrical structures, depending on the flow of gas on the substrate inside the reactor.
The basic structure of CVD devices is described with reference to FIG. 2. A substrate holder 53 equipped with an electrostatic attraction plate 52 is provided at the bottom of a reactor 51, and a shower electrode 54 is provided at the top. The shower electrode and the reactor which is maintained at ground potential are electrically insulated by an insulator 55. The substrate holder 53 is equipped with a substrate elevating and lowering device consisting of a lift pin 56, support plate 57, and vertical drive mechanism 58, as well as a heating mechanism consisting of a heater 59, a thermocouple 60, and heat control mechanism 61. The electrostatic attraction plate and substrate are heated to the desired temperature by the heating mechanism. The electrostatic attraction plate 52 is connected to an electrostatic attraction plate control power source 62, and is controlled by this power source. The electrostatic attraction plate 52 fixes the substrate 63 by electrostatic attraction force. The shower electrode 54 is connected to a reaction gas feed mechanism 64, and is electrically connected through a matching circuit 65 to a high frequency power source 66. The shower electrode 54 functions as a reaction gas feed component in the case of thermal CVD, and as a high frequency power supply port from the high frequency power source 66 in the case of plasma CVD.
In the case of thermal CVD, the temperature of the substrate 63 is stabilized to the desired temperature, a constant amount of reaction gas is fed from the shower electrode 54, and the desired thin film is deposited on the substrate on the basis of a chemical reaction.
In the case of plasma CVD, plasma is produced between the high frequency power-supplying shower electrode 54 and the substrate 63 and substrate holder 53, and the desired thin film is deposited on the substrate by a plasma enhanced chemical reaction.
During the aforementioned film deposition, film adheres to the inside surface of the reactor 51 in addition to the upper surface of the substrate 63. Removal of such film results in contaminating particles and lowers the semiconductor manufacturing yield. Films are thus usually removed by in-situ plasma cleaning every few substrate processings. During this plasma cleaning, a cleaning gas is introduced from a cleaning gas feed mechanism 74 by way of the shower electrode 54, and high frequency power is applied to the shower electrode 54 to produce a plasma inside the reactor.
When a thin film is deposited on the substrate 63 by the aforementioned CVD device, unreacted gas or byproduct gas results. The reactor 51 is equipped with a pump mechanism which actually pumps out the unreacted gas or side-reaction gas to the outside. FIG. 2 is an example in which a pump mechanism 67A is provided at the floor of the reactor 51. The pump mechanism 67A is formed of a plurality of connecting ports 75 formed in the reactor, a plurality of pipes 76 connected to the connecting ports 75, a gate valve 69, a container 70 housing the gate valve 69, a pump suction port 71, a pump 72 such as a turbo molecular pump, and an auxiliary pump mechanism 73. Other pump mechanism mounting locations include locations on the outside of the sidewalls of the reactor 51, indicated by the imaginary line 67. The pump mechanism 67A is connected to the connecting hole formed in the reactor.
The mounting locations for the pump mechanism in conventional CVD devices are described in view of the aforementioned asymmetrical and symmetrical structures.
As noted above, locations on the surrounding sidewalls (pump mechanism 67) as well as locations on the floor walls (pump mechanism 67A) can normally be considered as locations for mounting the pump mechanism on the reactor 51, depending on the design of the reactor.
In conventional structures where the pump mechanism 67 is located at the surrounding sidewall, the flow of gas on the substrate 63 is asymmetrical because the connecting hole 68 through which the gas is pumped out is partially offset. As such, this is not used except in processing devices intended for reactions in molecular flow regions of no more than 10.sup.-3 torr. When the gas flow is asymmetrical, the film uniformity or yield is adversely affected because gas flow determines the distribution of starting material gas and by-products in the reactor during film deposition by CVD. When gas flow to the substrate 63 is asymmetrical, the distribution of the film deposited on the substrate is asymmetrical according to the flow of gas. If there are parts where the circulating gas settles, deposition of reaction by-products tends to occur in these parts, causing dust and lowering the yield. Product deposition tends to result, and dust tends to be produced because of relatively greater concentrations of unreacted source gas or by-products in locations where the flow of gas from the connecting port 68 is concentrated. The structure of the reactor has accordingly been designed upon consideration of the flow of gas on the substrate in CVD devices. It is particularly important to ensure symmetrical gas flow on the substrate and to avoid gas flow with settling inside the reactor. For these reasons, it is undesirable for the structure to have the pump mechanism 67 in a location in part of the surrounding sidewall of the reactor 51.
Meanwhile, when the pump mechanism 67A is set up in the floor wall, a plurality of connecting holes 75 are generally formed equidistantly in the floor wall around the substrate holder 53, so as to allow a symmetrical gas flow to be readily created on the substrate. In this case a plurality of pipes 76 are connected to connecting ports 75. The floor wall part is generally used in the case of a viscous flow region. This has the abovementioned technical advantages and so the provision of a pump mechanism at the floor wall is preferred.
Examples of other structures for when the pump mechanism 67A is set up in the floor wall include those in which a perforated plate (indicated by broken line 77 in FIG. 2) is provided between the substrate holder 53 and the surrounding sidewalls, so that the gas flow is uniformly symmetrical. In the perforated plate 77, the number of holes or the hole diameter is designed to increase from the side on which the connecting ports are present toward the opposite wall, so as to achieve better symmetry. Even just one connecting port (or pipe connected thereto) formed around the substrate holder may be used in this case. The advantage of this structure is that the connecting port and pipe are one assembly by themselves.
The following problems come up in conventional CVD devices in which symmetrical gas flow on the substrate can be realized, that is, CVD devices in which pumping is effected from the floor wall component.
In the structure in which a plurality of connecting ports 75 are formed in the floor wall, and a plurality of pipes 76 from the outside are connected to these connecting ports, the plurality of pipes surround the drive mechanism used to convey or to elevate and lower the substrate, complicating the hardware structure of the reactor. The structure compromises the reactor maintenance, which in turn leads to lower equipment operationality.
The piping components are susceptible to concentrations of unreacted reaction gas and by-products, resulting in pronounced film adhesion. It is difficult to remove the film adhering to the piping components through plasma cleaning, making it necessary to manually clean them during maintenance. Maintenance requires the removal of the piping to clean it. Since a great deal of time is needed to remove the piping, such maintenance is even more cumbersome.
In the structure that is equipped with a perforated plate 77, film tends to adhere to or by-products tend to accumulate on the floor wall or perforated plate 77. Such film and by-products are not readily removed because it is difficult to direct the plasma to the floor wall or the inside of the holes of the perforated plate. They thus become a source of dust, which lowers the element manufacturing yield. The holes of the perforated plate cause abnormal discharge (holocathode discharge) during the deposition of films by plasma CVD or during cleaning in thermal CVD. As a result, more film adheres to the perforated plate, and the accumulated material is scattered, causing more dust.